US8830480B2ActiveUtilityPatentIndex 31
Measurement apparatus
Est. expiryNov 10, 2030(~4.4 yrs left)· nominal 20-yr term from priority
G01B 9/02076G01B 9/0207G01B 9/02003G01B 9/02067G01B 9/02005
31
PatentIndex Score
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Cited by
10
References
8
Claims
Abstract
The present invention provides a measurement apparatus which measures a distance between a reference surface and a surface to be measured, including a wavelength reference element configured to include a gas cell in which a plurality of types of gases having absorption lines different from each other are sealed, and a processing unit configured to set a wavelength of light emitted by a light source to a plurality of different wavelengths corresponding to a plurality of different absorption lines by using the wavelength reference element, control a phase detection unit to detect a phase corresponding to an optical path length between the reference surface and the surface to be measured for each of the plurality of different wavelengths, and perform processing of obtaining the distance.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1. A measurement apparatus which measures a distance between a reference surface and a surface to be measured, comprising:
a wavelength reference element configured to include a gas cell in which a plurality of types of gases having absorption lines different from each other are sealed;
a light splitting element configured to split light emitted by a light source into a first light beam and a second light beam, and cause the first light beam to enter the reference surface and the second light beam to enter the surface to be measured;
a phase detection unit configured to detect interference light between the first light beam reflected by the reference surface and the second light beam reflected by the surface to be measured, and detect, from a signal of the interference light, a phase corresponding to an optical path length between the reference surface and the surface to be measured; and
a processing unit configured to set a wavelength of light emitted by the light source to a plurality of different wavelengths corresponding to a plurality of different absorption lines by using the wavelength reference element, control the phase detection unit to detect a phase corresponding to the optical path length between the reference surface and the surface to be measured for each of the plurality of different wavelengths, and perform processing of obtaining the distance,
wherein the plurality of different wavelengths include a first reference wavelength, a second reference wavelength, a third reference wavelength, and a fourth reference wavelength,
letting λ 1 be the first reference wavelength, λ 2 be the second reference wavelength, λ 3 be the third reference wavelength, λ 4 be the fourth reference wavelength, φ 1 be a phase detected by the phase detection unit at the first reference wavelength, φ 2 be a phase detected by the phase detection unit at the second reference wavelength, φ 3 be a phase detected by the phase detection unit at the third reference wavelength, φ 4 be a phase detected by the phase detection unit at the fourth reference wavelength, Λ 12v be a wavelength, in vacuum, of a synthetic wavelength of the first reference wavelength and the second reference wavelength represented by λ 1 ·λ 2 /|λ 2 −λ 1 |, Λ 23v be a wavelength, in vacuum, of a synthetic wavelength of the second reference wavelength and the third reference wavelength represented by λ 2 ·λ 3 /|λ 3 −λ 2 |, Λ 34v be a wavelength, in vacuum, of a synthetic wavelength of the third reference wavelength and the fourth reference wavelength represented by λ 3 ·λ 4 /|λ 4 −λ 3 |, and Λ 4v be a wavelength of the fourth reference wavelength in vacuum, the processing unit obtains a distance D in accordance with
D
=
λ
4
v
2
(
round
(
2
D
34
λ
4
v
-
ϕ
4
2
π
)
+
ϕ
4
2
π
)
D
34
=
Λ
34
v
2
(
round
(
2
D
23
Λ
34
v
-
ϕ
3
-
ϕ
4
2
π
)
+
ϕ
3
-
ϕ
4
2
π
)
D
23
=
Λ
23
v
2
(
round
(
2
D
12
Λ
23
v
-
ϕ
2
-
ϕ
3
2
π
)
+
ϕ
2
-
ϕ
3
2
π
)
D
12
=
Λ
12
v
4
π
(
ϕ
1
-
ϕ
2
)
.
2. A measurement apparatus which measures a distance between a reference surface and a surface to be measured, comprising:
a wavelength reference element configured to include a gas cell in which a plurality of types of gases having absorption lines different from each other are sealed;
a light splitting element configured to split light emitted by a light source into a first light beam and a second light beam, and cause the first light beam to enter the reference surface and the second light beam to enter the surface to be measured;
a phase detection unit configured to detect interference light between the first light beam reflected by the reference surface and the second light beam reflected by the surface to be measured, and detect, from a signal of the interference light, a phase corresponding to an optical path length between the reference surface and the surface to be measured; and
a processing unit configured to set a wavelength of light emitted by the light source to a plurality of different wavelengths corresponding to a plurality of different absorption lines by using the wavelength reference element, control the phase detection unit to detect a phase corresponding to the optical path length between the reference surface and the surface to be measured for each of the plurality of different wavelengths, and perform processing of obtaining the distance,
wherein the plurality of different wavelengths include a first reference wavelength, a second reference wavelength, and a third reference wavelength,
the processing unit controls the phase detection unit to detect a phase corresponding to the optical path length between the reference surface and the surface to be measured for each of the first reference wavelength, the second reference wavelength, and the third reference wavelength while continuously changing a wavelength of light emitted by the light source from the first reference wavelength to the second reference wavelength by using the wavelength reference element, and
letting λ 1 be the first reference wavelength, λ 2 be the second reference wavelength, λ 3 be the third reference wavelength, Φ 1 be a phase detected by the phase detection unit at the first reference wavelength, Φ 2 be a phase detected by the phase detection unit at the second reference wavelength, Φ 3 be a phase detected by the phase detection unit at the third reference wavelength, M be the number of phase jumps generated upon continuously changing the wavelength of light emitted by the light source from the first reference wavelength to the second reference wavelength, Λ 12 be a synthetic wavelength of the first reference wavelength and the second reference wavelength represented by λ 1 ·λ 2 /|λ 2 −λ 1 |, Λ 13 be a synthetic wavelength of the first reference wavelength and the third reference wavelength represented by λ 1 ·λ 3 /|λ 3 −λ 1 |, n 3 be a refractive index of λ 3 in a space between the reference surface and the surface to be measured, n 12 be a group index for λ 1 and λ 2 , and n 13 be a group index for λ 1 and λ 3 , the processing unit obtains a distance D in accordance with
D
1
=
Λ
12
2
n
12
(
M
+
ϕ
2
-
ϕ
1
2
π
)
D
=
λ
3
2
n
3
(
round
(
n
3
n
13
Λ
13
λ
3
(
round
(
n
13
n
12
2
D
1
Λ
13
-
ϕ
3
-
ϕ
1
2
π
)
+
ϕ
3
-
ϕ
1
2
π
)
-
ϕ
3
2
π
)
+
ϕ
3
2
π
)
.
3. The apparatus according to claim 2 , wherein a lower absorptance out of an absorptance of an absorption line corresponding to the first reference wavelength and an absorptance of an absorption line corresponding to the second reference wavelength is lower than an absorptance of an absorption line corresponding to the third reference wavelength.
4. The apparatus according to claim 1 , wherein
the gas cell includes a first gas cell in which at least a gas having a first absorption line and a gas having a second absorption line are sealed, and a second gas cell in which at least a gas having a third absorption line is sealed, and
the first absorption line, the second absorption line, and the third absorption line satisfy a relation:
wavelength corresponding to the first absorption line<wavelength corresponding to the third absorption line<wavelength corresponding to the second absorption line.
5. The apparatus according to claim 1 , wherein at least two of acetylene, an acetylene isotope, hydrogen cyanide, and a hydrogen cyanide isotope are sealed in the gas cell.
6. A measurement apparatus which measures a distance between a reference surface and a surface to be measured, comprising:
a wavelength reference element configured to include a plurality of gas cells in which a gas having an absorption line is sealed;
a light splitting element configured to split light emitted by a light source into a first light beam and a second light beam, and cause the first light beam to enter the reference surface and the second light beam to enter the surface to be measured;
a phase detection unit configured to detect interference light between the first light beam reflected by the reference surface and the second light beam reflected by the surface to be measured, and detect, from a signal of the interference light, a phase corresponding to an optical path length between the reference surface and the surface to be measured; and
a processing unit configured to set a wavelength of light emitted by the light source to a plurality of different wavelengths corresponding to a plurality of different absorption lines by using the wavelength reference element, control the phase detection unit to detect a phase corresponding to the optical path length between the reference surface and the surface to be measured for each of the plurality of different wavelengths, and perform processing of obtaining the distance,
wherein a single type of gas is sealed in each of the plurality of gas cells,
the single types of gases respectively sealed in the plurality of gas cells have absorption lines different from each other,
the plurality of different wavelengths include a first reference wavelength, a second reference wavelength, and a third reference wavelength,
the processing unit controls the phase detection unit to detect a phase corresponding to the optical path length between the reference surface and the surface to be measured for each of the first reference wavelength, the second reference wavelength, and the third reference wavelength while continuously changing a wavelength of light emitted by the light source from the first reference wavelength to the second reference wavelength by using the wavelength reference element, and
letting λ 1 be the first reference wavelength, λ 2 be the second reference wavelength, λ 3 be the third reference wavelength, φ 1 be a phase detected by the phase detection unit at the first reference wavelength, φ 2 be a phase detected by the phase detection unit at the second reference wavelength, φ 3 be a phase detected by the phase detection unit at the third reference wavelength, M be the number of phase lumps generated upon continuously changing the wavelength of light emitted by the light source from the first reference wavelength to the second reference wavelength, Λ 12 be a synthetic wavelength of the first reference wavelength and the second reference wavelength represented by λ 1 ·λ 2 /|λ 2 −λ 1 |, Λ 13 be a synthetic wavelength of the first reference wavelength and the third reference wavelength represented by λ 1 ·λ 3 /|λ 3 −λ 1 |, n 3 be a refractive index of λ 3 in a space between the reference surface and the surface to be measured, n 12 be a group index for λ 1 and λ 2 , and n 13 be a group index for λ 1 and λ 3 , the processing unit obtains a distance D in accordance with
D
1
=
Λ
12
2
n
12
(
M
+
ϕ
2
-
ϕ
1
2
π
)
D
=
λ
3
2
n
3
(
round
(
n
3
n
13
Λ
13
λ
3
(
round
(
n
13
n
12
2
D
1
Λ
13
-
ϕ
3
-
ϕ
1
2
π
)
+
ϕ
3
-
ϕ
1
2
π
)
-
ϕ
3
2
π
)
+
ϕ
3
2
π
)
.
7. The apparatus according to claim 6 , wherein a lower absorptance out of an absorptance of an absorption line corresponding to the first reference wavelength and an absorptance of an absorption line corresponding to the second reference wavelength is lower than an absorptance of an absorption line corresponding to the third reference wavelength.
8. The apparatus according to claim 6 , wherein at least two of acetylene, an acetylene isotope, hydrogen cyanide, and a hydrogen cyanide isotope are respectively sealed in the plurality of gas cells.Cited by (0)
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